In this type of technical field, there is a technology about pulse width modulation (PWM) control of an inverter (e.g. refer to a patent document 1). According to an apparatus disclosed in the patent document 1, by correcting a PWM signal with a correction signal generator for outputting a correction signal having a symmetric waveform to that of an alternating current output, a waveform of a three-phase alternating current output supplied to a load is corrected in a positively and negatively symmetrical manner, and waveform distortion due to a harmonic can be suppressed.
Incidentally, there is also suggested an apparatus for reducing direct current ripple superimposed on a direct current output voltage (e.g. refer to a patent document 2).